Field of the Disclosure
This disclosure relates to superconductors, specifically to efficient methods of fabricating superconducting articles.
Background
Several materials and systems are being developed to solve the looming problems with energy generation, transmission, conversion, storage, and use. Superconductors may be a unique system solution across a broad spectrum of energy problems. Generally, superconductors enable high efficiencies in generators, power transmission cables, motors, transformers and energy storage. Further, superconductors have applications beyond energy, such as medicine, particle physics, communications, and transportation.
The superconductors are configured into various articles including wires, tapes, and other elongate structures for energy transmission. In some instances, these elongate superconducting articles are generally configured as superconducting tapes. Superconducting tapes are being developed, some of which include epitaxial, single-crystal-like thin films on polycrystalline substrates.
Generally, there are about 9 components in a typical second-generation (2G) High Temperature Superconductor (HTS) wire. There have been several different approaches are used to manufacture 2G HTS wire. In one instance, a biaxially-textured buffer layer is deposited on a substrate, typically made of a flexible metal such as a nickel alloy. The biaxially-textured buffer can be achieved by technique known in the art as Ion Beam Assisted Deposition (IBAD), Rolling Assisted Biaxially Textured Substrates (RABiTS), and Inclined Substrate Deposition (ISD). The superconductor film is deposited on the buffer layer by processes such as metal organic-chemical vapor deposition (MO-CVD), metal organic deposition (MOD), pulsed laser deposition (PLD) and electron-beam evaporation. Regardless of the method used to achieve biaxial texture, or the processes used for buffer or superconductor deposition, or the materials used for substrate, buffer, and superconductor, 2G HTS wire manufacturing of 2G HTS wire involves deposition of a silver over-layer atop the superconductor, followed by oxygenation heat treatment in an oxygen ambient.
In some instances, the wire manufacturing can include additional steps such as slitting, deposition of silver and further rounds of oxygenation heat treatment. Silver deposition is typically conducted by magnetron sputtering or evaporation. In some other instances, copper stabilizer may be applied over the silver layer prior to slitting or over the second silver over-layer after slitting. Electroplating, Electroless plating, lamination or other bonding techniques may be used to apply the copper stabilizer. Certain superconducting films that are processed by this technique exhibit critical current densities comparable to that achieved in epitaxial films grown on single crystal substrates. Using this technique, companies have demonstrated pilot-scale manufacturing of superconducting composite tapes. These tapes form a single crystal-like epitaxial film that is now being manufactured in lengths over a kilometer using a polycrystalline substrate base.
However, the most expensive step is deposition of the superconducting film, and the product becomes a high value added product after this step. Any yield loss after this step can have a significant negative impact on manufacturing cost, throughput, and efficiency. Furthermore, if the step of oxygenation is not conducted in a reel-to-reel mode, it requires substantial manual handling during which the high-value-added product is prone to damage and hence yield loss. Additionally, each of the two conventional oxygenation steps typically requires more than 20 hours, including handling time, and adds substantial time to manufacturing process.